Genetic Variation and Distribution of Pacific Crabapple
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J. AMER.SOC.HORT.SCI. 137(5):325–332. 2012. Genetic Variation and Distribution of Pacific Crabapple Kanin J. Routson1 University of Arizona, Arid Lands Resource Sciences, 1955 East Sixth Street, P.O. Box 210184, Tucson, AZ 85719 Gayle M. Volk and Christopher M. Richards National Center for Genetic Resources Preservation, U.S. Department of Agriculture, 1111 S. Mason Street, Fort Collins, CO 80521 Steven E. Smith School of Natural Resources and the Environment, University of Arizona, P.O. Box 210043, Tucson, AZ 85721 Gary Paul Nabhan The Southwest Center and School of Geography and Development, University of Arizona, 1052 N. Highland Avenue, Tucson, AZ 85721 Victoria Wyllie de Echeverria School of Environmental Studies, University of Victoria, P.O. Box 3060 STN CSC, Victoria, British Columbia V8W 3R4, Canada ADDITIONAL INDEX WORDS. species distribution modeling, genetic diversity, Malus fusca, ex situ gene conservation ABSTRACT.Pacificcrabapple[Malus fusca (Raf.) C.K. Schneid.] is found in mesic coastal habitats in Pacific northwestern North America. It is one of four apple species native to North America. M. fusca is culturally important to First Nations of the region who value and use the fruit of this species as food, bark and leaves for medicine, and wood for making tools and in construction. However, little is known about either distribution or genetic diversity of this species. To correct this deficiency, we used habitat suitability modeling to map M. fusca habitat types with species occurrence records. The species apparently occupies at least two distinct climate regions: a colder, drier northern region and a warmer, wetter southern region. Total area of modeled habitat encompasses ’356,780 km2 of low-lying areas along the Pacific coast. A total of 239 M. fusca individuals sampled from across its native range were genetically compared using six microsatellite markers to assess for possible geographic structuring of genotypes. The primers amplified 50 alleles. Significant isolation by distance was identified across the ’2600 km (straight line) where samples were distributed. These results may help establish priorities for in situ and ex situ M. fusca conservation. Wild apple species (Malus Mill.) are native throughout Minnesota to Texas. These have been determined to be closely temperate climes of Asia, Europe, and North America (Brown, related based on isozymes (Dickson et al., 1991). The species 2012; Luby, 2003). They offer promising sources of genetic native to the Pacific northwestern North America, M. fusca, diversity for apple breeding (Brown, 2012) and also provide is the sole geographic, morphological (Van Eseltine, 1933), a wildlife habitat and serve as a direct food source for humans. chemical (Williams, 1982), and genetic outlier among the North Four Malus species are native to North America. Three species American taxa. occur in eastern and midwestern United States and eastern Pacific crabapple is a small, deciduous, often multitrunked Canada: M. angustifolia (Aiton) Michx. is native from southern tree or thicket-forming shrub that occurs naturally in mesic New Jersey to Florida, M. coronaria (L.) Mill. from Ontario to environments along river bottoms, meadows, and muskeg South Carolina, and M. ioensis Alph. Wood Britton ranges from fringes at low to mid-elevations along the Pacific coast of North America from northern California to the Kenai Peninsula Received for publication 29 May 2012. Accepted for publication 12 July 2012. in Alaska (Viereck and Little, 1986). Yellow to red fruit are We sincerely thank all who have contributed to the success of this research. We oblong and 1 to 2 cm in length (Fig. 1). It groups genetically specifically acknowledge our British Columbia collaborators Nancy Turner, with the species native to central Asia and China rather than the Leslie Main Johnson, and Ken Downs for their insights samples from the region. other North American taxa, according to amplified fragment Thanks to Phillip Jenkins and Sarah Hunkins at the University of Arizona length polymorphism data (Qian et al., 2006) and nuclear Herbarium (ARIZ) for assistance with herbarium records and Steffi Ickert-Bond at the University of Alaska Museum of the North Herbarium (ALA) and staff at ribosomal and chloroplast DNA (Robinson et al., 2001). M. fusca the University of British Columbia Herbarium (UBC) and University of Alberta is considered to be in section Kansuenses Rehd. along with Herbarium (ALTA) for specimens. Thanks to Sarah Hayes, Joseph Postman, M. kansuensis (Batalin) C.K. Schneid., M. toringoides (Rehder) and all who helped with sample collection. Thanks to Adam Henk for technical Hughes, and M. transitoria (Batalin) C.K. Schneid. (Robinson assistance in the laboratory and Ned Garvey and Karen Williams for securing Plant Germplasm Collection funds. Finally, thanks to the Kellogg Program of et al., 2001). Because of genetic grouping with central Asia, the the University of Arizona Southwest Center for funding. species is hypothesized to be a recent migrant across the Bering 1Corresponding author. E-mail: [email protected]. Strait (Williams, 1982). J. AMER.SOC.HORT.SCI. 137(5):325–332. 2012. 325 Materials and Methods SAMPLE COLLECTIONS. Two hundred thirty-nine M. fusca individuals were sam- pled across the species’ native range from southeastern Alaska to northern California. Samples were obtained from field collections (138 individuals from California, Oregon, Washington, and British Columbia), herbar- ium specimens (65 individuals from Alaska and British Columbia), and U.S. Department of Agriculture (USDA) germplasm accessions (36 individuals from California, Oregon, and Washington). The latter were obtained from the USDA Agricultural Research Service Plant Genetic Resources Unit (PGRU) collec- tion in Geneva, NY. The University of Alaska Museum of the North Herbarium and Univer- sity of British Columbia Herbarium provided herbarium specimens. Field collections took place Oct. 2010. Collections were made in publicly accessible parks, natural areas, and roadsides in moist, coastal habitats. Fresh leaf tissue was sam- pled (generally five leaves per tree) for genetic analysis. The fresh leaves were stored in plastic bags and keptcooluntiltissue samples were sent to the laboratory. There they were loaded into DNA extraction plates, after which they were frozen at –80 °C for long-term storage. General physical site characteristics, habitat type, associated veg- etation, and locality descriptions were docu- mented and photographs taken at each site. Latitude/longitude coordinates and elevation were recorded for individual trees during Fig. 1. Images of Malus fusca fruit collected from trees in (A) Washington and (B) California. field collections using a handheld GPS (eTrex-Vista; Garmin, Olathe, KS). Herbar- Malus fusca can serve as a rootstock for domesticated apple ium vouchers were collected at six sites and sent to the trees in waterlogged sites (R. Duncan, personal communica- University of Arizona and University of Washington herbariums. tion) and remains a culturally important species for First Na- Locations for herbarium specimens and USDA accessions were tions of the Pacific northwestern North America (Downs, 2006; verified by comparing collection notes with Google Earth (Ver- McDonald, 2005; Turner and Turner, 2008). All parts of the tree sion 6.2; Google, Mountain View, CA) and biogeoreferencing have been used including the fruit as food, the bark and leaves web application GEOLocate Web (Rios and Bart, 2005). Points for medicines, and the dense wood for implements and in con- were selected based on habitat characteristics and descrip- struction (Turner and Bell, 1971a, 1971b). It is well docu- tions of the localities. Specimens with less than a 5000-m un- mented that Haida, Tsimshian, Tlingit, and Wakashan peoples certainty in GEOLocate were included in the species distribution in British Columbia and southeastern Alaska have tended small modeling. orchards of M. fusca that were often owned and managed in SPECIES DISTRIBUTION MODELING. A SDM for M. fusca was ways that were passed down between generations (Deur and created using MaxEnt software [Version 3.3.3 (Phillips et al., Turner, 2005; Downs, 2006; McDonald, 2005; Turner and 2006)] and WorldClim 1.4 spatially interpolated climate grids Peacock, 2005; Turner and Turner, 2008). Diploid M. fusca (Hijmans et al., 2005) and M. fusca collection localities (n = 205 hybridizes with M. ·domestica Borkh. (Hartman, 1929) and with less than 5000-m uncertainty) and M. fusca occurrence has been a source of fire blight (Erwinia amylovora Burrill) records (n = 152 with less than 5000-m uncertainty) from the resistance in apple breeding programs that use transgenic Global Biodiversity Information Facility (2001). We used early flowering methods to reduce the length of the generation 1950–2000 data at a 30-arc second resolution ( 0.56 km2 at cycles (Flachowsky et al., 2011). lat. 49° N) for elevation and 19 bioclimatic variables based on We describe genetic diversity and distribution of M. fusca monthly precipitation and temperature. American Standard through species distribution modeling (SDM) of known occur- Code for Information Interchange (ASCII) files were generated rence records and genetic fingerprinting of 239 M. fusca in DIVA-GIS [Version 7.5.0 (Hijmans et al., 2001)] from individuals sampled from northern California to southeastern WorldClim data for the Pacific northwestern North America Alaska using six microsatellite markers. region (long. 121.0° W to 151.0°